Synthesis of Lactic Acid-Based Thermosetting Resins and Their Ageing and Biodegradability.

Lara Lopes Gomes Hastenreiter,Dan Åkesson,Anilkumar Yadav,Sunil Kumar Ramamoorthy,Rajiv K Srivastava,Akram Zamani

doi:10.3390/polym12122849

Lara Lopes Gomes Hastenreiter, Dan Åkesson + Show 4 more

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https://doi.org/10.3390/polym12122849

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Abstract

The present work is focused on the synthesis of bio-based thermoset polymers and their thermo–oxidative ageing and biodegradability. Toward this aim, bio-based thermoset resins with different chemical architectures were synthesized from lactic acid by direct condensation with ethylene glycol, glycerol and pentaerythritol. The resulting branched molecules with chain lengths (n) of three were then end-functionalized with methacrylic anhydride. The chemical structures of the synthesized lactic acid derivatives were confirmed by proton nuclear magnetic resonance spectroscopy (1H-NMR) and Fourier transform infrared spectroscopy (FT–IR) before curing. To evaluate the effects of structure on their properties, the samples were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and the tensile testing. The samples went through thermo-oxidative ageing and biodegradation; and their effects were investigated. FT-IR and 1H-NMR results showed that three different bio-based resins were synthesized using polycondensation and end-functionalization. Lactic acid derivatives showed great potential to be used as matrixes in polymer composites. The glass transition temperature of the cured resins ranged between 44 and 52 °C. Pentaerythritol/lactic acid cured resin had the highest tensile modulus and it was the most thermally stable among all three resins. Degradative processes during ageing of the samples lead to the changes in chemical structures and the variations in Young’s modulus. Microscopic images showed the macro-scale surface degradation on a soil burial test.

Highlights

Bio-based polymers, prepared from renewable resources, have been of much interest to researchers from both the academic sector and industries, in order to find a substitute for petroleum-based polymers
In an attempt to decrease the dependency on fossil resources, polymer researchers have been rapidly developing bio-based thermoplastics
In comparison with the rapid developments in bio-based thermoplastics, considerably less research has been done on bio-based thermosets

Summary

Introduction

Bio-based polymers, prepared from renewable resources, have been of much interest to researchers from both the academic sector and industries, in order to find a substitute for petroleum-based polymers. The extensive use of fossil resources and the dependence on them is becoming an issue in the polymer industry owing to the challenges brought about by the fast depletion of the fossil resources, the frequent price fluctuations and the increasing demand for sustainable materials. Fossil resources-based polymers raise several environmental concerns, namely, those of sustainability, carbon dioxide emissions, disposal and recyclability. In an attempt to decrease the dependency on fossil resources, polymer researchers have been rapidly developing bio-based thermoplastics. In comparison with the rapid developments in bio-based thermoplastics, considerably less research has been done on bio-based thermosets.

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